[PATCH 5.10 350/406] net: ipv6/addrconf: avoid integer underflow in ipv6_create_tempaddr

Greg Kroah-Hartman
2023-09-17T19:40:12Z

From: Alex Henrie <alexhenrie24@gmail.com>

[ Upstream commit f31867d0d9d82af757c1e0178b659438f4c1ea3c ]

The existing code incorrectly casted a negative value (the result of a
subtraction) to an unsigned value without checking. For example, if
/proc/sys/net/ipv6/conf/*/temp_prefered_lft was set to 1, the preferred
lifetime would jump to 4 billion seconds. On my machine and network the
shortest lifetime that avoided underflow was 3 seconds.

Fixes: 76506a986dc3 ("IPv6: fix DESYNC_FACTOR")
Signed-off-by: Alex Henrie <alexhenrie24@gmail.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/ipv6/addrconf.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 9b414681500a5..0eafe26c05f77 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -1359,7 +1359,7 @@ static int ipv6_create_tempaddr(struct inet6_ifaddr *ifp, bool block)
* idev->desync_factor if it's larger
*/
cnf_temp_preferred_lft = READ_ONCE(idev->cnf.temp_prefered_lft);
- max_desync_factor = min_t(__u32,
+ max_desync_factor = min_t(long,
idev->cnf.max_desync_factor,
cnf_temp_preferred_lft - regen_advance);

--
2.40.1